The ground surfaces of a moon and planets are usually not stable ground. Instead, such ground surfaces are usually covered by sand, and thus have poor bearing power. Further, when a vehicle travels on the moon and planets on which the gravity is lower than that on earth, it is necessary to distribute the weight of the vehicle over a wide area, and to lower the pressure contacting the ground when traveling.
One type of prior art space exploration vehicle has four to eight cylindrical wheels for enabling wide a ground area to be contacted. In such vehicle having wheels, the pressure contacting the ground is at a maximum under the wheels. Thus, the wheels are likely to be buried under the sand, and it would be difficult to continue traveling.
One type of combat car or construction vehicle is a crawler type vehicle which comprises a driving wheel, idler wheels and a crawler belt spooled over the driving wheel and the idler wheel, and travels on the ground using the crawler belt. The crawler type vehicle contacts a wide area of ground, and thus has a good traveling capability even on a soft ground.
The crawler type traveling device comprises a crawler belt having a plurality of crawler plates made of a rigid metal, the crawler plates being pivotally connected to adjacent plates by pins. The crawler belt goes around the driving wheel and the idler wheels. Another crawler belt is made of a rubber having flexibility, and does not have crawler plates connected by pins.
Under a vacuum or low pressure atmosphere on the moon or planets, pin portions which connect the crawler plates have poor lubricity, and thus have much friction. Thus, durability is degraded.
The crawler belt made of rubber exhausts much gas out of the belt and is easily degraded, and thus it is not suitable to use in space.
Further, a crawler type vehicle needs a lot of rotating wheel mechanisms for equalizing the pressure contacting the ground. Thus this mechanism is complicated and heavy, and reliability is degraded thereby.
Patent Document 1 (JP 2005-111595) discloses a crawler type traveling robot comprising a base, a crawler provided on each of the right and left sides of the base, and an arm provided on the base. Each crawler comprises a driving wheel provided at one end thereof in a longitudinal direction, a traveling motor for driving the driving wheel, an idling wheel provided at the other end thereof in a longitudinal direction, an endless track engaging the driving wheel and idling wheel and spooled around both wheels, a center wheel engaging the endless track at the center portion of the crawler and a central motor for driving the center wheel.
However, the crawler type traveling robot shown in patent document 1 does not contact the ground with uniform pressure. Further, there is a possibility that stones or sand will easily enter into the engaging portions of the crawler belt and the driving wheel.
Patent Document 1: JP 2005-111595